1. Field of the Invention
This invention relates to a process and apparatus for removing deposits such as tungsten from the backside and end edge of a semiconductor wafer. More particularly, this invention relates to a process and apparatus for removing such deposits with a plasma etch while retaining the semiconductor wafer in a position adjacent to, but spaced from the faceplate in a plasma deposition apparatus.
2. Description of the Related Art
In the processing of a wafer or substrate in the prior art, the wafer has been spaced from a support plate at times for various reasons. For example, Gillery U.S. Pat. No. 3,907,660 teaches the cathode sputtering of a metal onto a glass substrate to form a transparent electroconductive coating. An anode plate supports a series of posts arranged in checkerboard fashion to support one or more glass sheets during the cathode sputtering.
Whitlock et al U.S. Pat. No. 4,736,087 discloses a plasma stripping apparatus for removing photoresist from a wafer. The apparatus is provide with external electrodes including a cathode located near but below the top of a reactor chamber in the apparatus and an anode located near the bottom of the chamber but above the wafer to be stripped. On the chamber base is a wafer support chuck having a plurality of quarts pins on which a wafer rests during the stripping operation.
However, in the processing of semiconductor wafers, blanket deposition of a material such as tungsten over the upper or front surface of the wafer is sometimes carried out to form patterns of the deposited material over a masked semiconductor wafer. If the rear surface of the wafer is not protected, i.e., is spaced from the support plate as described above, it will also be covered with the deposited material which may later flake off, thereby creating undesirable particles which can interfere with subsequent processing, resulting in a lowering of the yield.
To prevent such deposition on the backside of the wafer from occurring, it has been the practice to clamp or seal the wafer to the backplate or support base (susceptor) to thereby eliminate or limit exposure of the rear surface of the semiconductor wafer. However, the materials used in the blanket deposition still coat the side or end edge of the wafer as well as depositing on the clamping means or clips used to secure the wafer to the backplate. Furthermore, the use of such clamping means results in the shielding of a portion of the front surface of the wafer, thereby reducing the total area of the front surface of the wafer on which integrated circuit structures may be formed.
It has previously been proposed by one of us, in Chang et al U.S. patent application Ser. No. 337,607, now issued U.S. Pat. No. 4,962,049 on Oct. 9, 1990 and assigned to the assignee of this invention, to use a plasma etch to remove unwanted deposits from the backside of a semiconductor wafer by raising the wafer off the susceptor or backplate a spaced distance and then forming a plasma in the gap between the wafer and the grounded susceptor to remove the deposits from the backside of the wafer. While this method will satisfactorily remove such unwanted backside deposits from the wafer, some of the materials on the front side of the wafer may also be inadvertently removed by the plasma during this removal step.
It would, therefore, be desirable to be able to remove such undesirable deposits from the backside and end edge of a semiconductor wafer while inhibiting removal of any materials from the front surface of the wafer during such a removal step.